The friction pressure of the existing friction-driven speed reduction device is preset and constant, the pressure is constant no matter how the load torque changes, which causes large friction loss in small torque, or may cause exceeding the preset torque, slipping and burning-out in large torque; and with the increase of friction loss, the torque of the system will become smaller and smaller, finally lose efficacy quickly; therefore, the industry hopes to develop a friction-driven speed reduction device that can automatically adjust the frictional pressure according to the magnitude of load torque.